The present invention relates to a vacuum degassing apparatus and more particularly to a vacuum degassing apparatus for use in a vacuum siphon degassing process or in a vacuum circulation degassing process.
It has been known that properties of a metal or an alloy can be considerably improved by treating it in a vacuum.
In the vacuum siphon degassing process (DH process), a vessel is evacuated with a tube extending from the bottom of the vessel immersed in a molten steel in a ladle. The molten steel is sucked up by the difference in pressure between the surrounding atmosphere and the inside of the vacuum vessel and is progressively degassed therein. By moving the vacuum vessel up and down the molten steel is repeatedly sucked into and discharged from the vessel to thereby make the degassing of the molten steel proceed.
In the vacuum circulation degassing process (RH process), the vessel is evacuated with two tubes extending from the bottom of the vessel immersed in the molten steel in the ladle. By injecting argon gas from the lower end of one of the tubes the molten steel is sucked into the vacuum vessel and degassed therein. The degassed molten steel returns to the ladle through the other tube.
Thus, the two degassing processes have the feature in common that the molten steel is made to circulate or flow between the ladle and the vacuum vessel and is degassed in the vacuum vessel. The apparatuses heretofore employed in these degassing processes were open to the atmosphere at the top of the ladle and, accordingly, had the disadvantage that gas would permeate into the molten steel in the ladle through the slag and reduce the degassing efficiency. In order to prevent the absorbing reaction of the molten steel with the gas from the atmosphere, it has been proposed that the vacuum vessel and the ladle should be contained within a sufficiently large container which is then either evacuated or filled with, for example, an inert gas prior to degassing treatment. This proposal is, however, not suitable because of the huge volume of the container which will require a high cost to build and a long period of time to replace the air within the container.
Accordingly, it is the object of the present invention to provide a vacuum degassing apparatus for use in a DH process or an RH process capable of economically preventing the reduction in degassing efficiency and effectively performing degassing treatment in a short period of time.